Is this tiny, 505-million-year-old creature the ancestor of all humans?

Nature · Published 3 October 2026 Swipe more like this →

In short: Deep in Canada’s Burgess Shale lies Pikaia gracilens, a small, eel-like animal that has sparked a century of scientific debate. Once dismissed as a simple worm, this fossil is now recognized as a foundational member of the chordate family, sharing the same basic blueprint as every vertebrate on Earth today.

Discovered in the Burgess Shale of British Columbia, Pikaia gracilens dates back approximately 505 million years to the Cambrian period. When American palaeontologist Charles Doolittle Walcott first described the creature in 1911, he classified it as a polychaete worm, noting its segmented body but struggling to place it within known annelid families. For decades, its true identity remained a mystery, with its status as a chordate—the phylum that includes fish, birds, and mammals—only gaining broad scientific acceptance after a detailed 2012 analysis by researchers including Simon Conway Morris and Jean-Bernard Caron.

The breakthrough came from examining 114 specimens using advanced imaging techniques like scanning electron microscopy. Researchers identified key anatomical signatures of chordates: a notochord, a dorsal nerve cord, and extensive myomeres—blocks of skeletal muscle tissue. These features, alongside a vascular system, confirm Pikaia as a primitive chordate. Averaging about five centimetres in length, the animal was laterally flattened and likely swam by moving its body in side-to-side curves above the sea floor.

While Pikaia is often celebrated as a distant relative of vertebrate ancestors, its exact position in the evolutionary tree remains a subject of nuance. Some researchers view it as a basal chordate or a stem-chordate, noting that it possesses primitive traits like a cuticle, which is more characteristic of invertebrates. Because Pikaia lacked mineralized bones, it would have vanished without a trace if not for the exceptional preservation conditions of the Burgess Shale. Its discovery provides a rare, humbling glimpse into the deep history of the chordate lineage, illustrating how a creature no longer than a thumb serves as a vital link in the story of vertebrate evolution.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• A 555-million-year-old worm might be your oldest relative
• A 560-million-year-old 'goo-filled bag' is rewriting early animal history
• The 375-million-year-old fish that gave humans shoulders and wrists
• For 70 years, scientists have been looking at this ancient fossil the wrong way
• The Tully Monster was a bizarre, ancient fish that defied classification for sixty years.
• How pit vipers use a sixth sense to hunt in total darkness
• Terror birds were not just monsters; they were the apex predators of Miocene Argentina
• The barrel-bodied giant that roamed the Triassic landscape like a prehistoric hippopotamus
• Terror birds were not just nightmares; they were the apex predators of the Cenozoic.
• These Triassic marine reptiles evolved unique metabolic strategies to survive in shallow waters
• The Philippine eagle is a legendary apex predator that once shaped the archipelago's creation.
• The Batfish: Why This Flat Reef Dweller Is Often Misidentified and Misnamed

More in Vertebrates · More in Nature · Latest · A–Z · All topics